In a similar boat although my new and noisy neighbours are in the other side of a semi detached.
The noises we hear are basically them shrieking really vile abuse at their kids (aged only 1 and 3), their awful dog (that never, ever gets walked and we live in the country) howling, and the woman's drunken/drug fuelled weird baying sounds. We all council tenants and the council's attitude was "It's social housing: what do you expect?" They are people housed from outside our area and from week one were paying bedroom tax (they told me) so don't even need a house that size. I have 5 kids, two disabled and the last family to get a 3 bed house here also had 5 kids, 1 child disabled. So it is the first time in a decade the council have re-housed people with two tiny kids in a house this size. Bizarre, when you hear how little housing stock (and sick that Selby District Council's attitude is "It's social housing: what do you expect?")
Social services came out after my kids and I overheard the man shouting particularly awful abuse at the baby. But seem to have signed them off after a couple of months of visiting them weekly.
Council say they will loan us a device that records sounds (apparently recording on your phone is unacceptable) but our problem is, the extreme abuse/domestic violence sounds are very brief bursts and very, very unpredicatable. By the time I'd found the thing and hit 'record' it would be over. And they only give you a couple of weeks to gather proof. The bloke had the cheek to get in first, claiming we slam doors. Council pointed out to him he was living in a furniture and carpet-less house. He was clearly just making a claim to pre-empt our's as neighbours they have had in the past can't not have complained about the child abuse/domestic violence noises.
We found out they had moved out from HA or council housing previously, as the man couldn't cope with living next door to people and had a perfectly adequate detached private rental til our council, bizarrely put them to the top of the waiting list. We know these idiots are Teflon, presumably because they are on full housing benefit so they are a guaranteed income. They pay the full rent on time so are presumably dream tenants, to the landlord. They only checked one reference from their last landlord so didn't even unearth the fact they had had to move previously for antisocial behaviour.
OP I suspect your landlord is also seeing pound signs. It's all they care about. You are a new tenant who has a nuisance caused by more established tenants and we are very established tenants whose lives have been made hell by new tenants. It's not the longevity of a tenancy, I suspect - but the fact that some tenants do not have to struggle to pay rent - it's all paid for these dicks next door to me. So the council don't care how much they upset tenants who have paid them thousands of pounds over years and years. It's not the fact you're new. It's probably just the fact these idiots are good payers.
I know it's not worth ringing the RSPCA about the scraggy, neglected dog next door. If no-one gives a feck about two kids under 4 - it's even more certain no-one really gives a feck about a dog.